Responding to a tweet about the Covid-19 pandemic on Tuesday, President Trump wrote, “We need the Wall more than ever!” Trump had made a similar assertion during a rally in South Carolina at the end of February. “One of the reasons the numbers are so good: We will do everything in our power to keep the infection and those carrying the infection from entering our country,” he said. “You’ve all seen the wall has gone up like magic.”
Despite Trump’s hard-liner immigration rhetoric, infectious diseases do not, in fact, respect or abide by borders. And the physical barriers at the southern United States border can’t perform any magic when it comes to stopping the spread of the novel coronavirus.
In fact, research has shown that travel bans in general have limited impact on slowing the spread of disease unless transmission is also on the decline within a community itself. The Trump administration has touted its move in January to bar foreign nationals who had recently visited China, the epicenter of the outbreak, from entering the US, and to mandate two-week quarantines for US citizens returning from China. Analysis of flu data, including details about the 2009 H1N1 influenza outbreak, indicate that while air travel restrictions can delay the spread of a disease—a worthwhile goal—they typically don’t halt transmission. This is partly because air travel bans often go into effect too late and aren’t strict enough to truly halt all movement. Meanwhile, transmission often expands in affected communities as a result of ground travel.
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New research on Covid-19 in particular found that international travel restrictions in and out of Chin